The present invention concerns formed materials mainly for personal care products like diapers, training pants, swim wear, absorbent underpants, adult incontinence products and feminine hygiene products. This material may also be useful for other applications such as, for example, in bandages and wound dressings, nursing pads and in veterinary and mortuary applications.
Personal care articles usually have multiple layers of material of some sort to absorb liquids from the body. These layers may include natural fibers, synthetic fibers and superabsorbent particles in varying proportions. When liquid such as urine is deposited into a personal care product like a diaper, it goes through the uppermost layers, typically a liner against the body and a xe2x80x9csurgexe2x80x9d or xe2x80x9cintakexe2x80x9d layer designed to provide temporary liquid holding capacity. The product may also have a xe2x80x9cdistributionxe2x80x9d layer designed to move liquid in the X and Y directions in order to utilize more of the absorbent core. After going through these upper layers, the urine enters the absorbent core portion of the product. The absorbent core permanently retains the liquid.
The functions of the layers mentioned above may each be performed by different layers or a layer may perform more than one function. The combination of more than one function in a single layer, however, generally results in a significant decrease in the performance of each of the functions.
Absorbent cores are typically composed of superabsorbent particles and/or pulp. A newer class of absorbents also uses a binder to improve wet stability and to ease converting into final products. Binders can be liquid adhesive or thermally activatable fibers typically present in amounts between 10 and 25 weight percent.
Superabsorbent particles absorb many times their weight in liquid and swell greatly as a result of being wetted. This swelling holds liquid within the product and so protects the wearer""s skin, clothing and bedding, but may also block the further intake of liquid. This occurs because the swollen particles become so large as to close off fluid entrances to the structure, a phenomenon known in the art as xe2x80x9cgel blockingxe2x80x9d.
Alternatively, an absorbent structure lacking superabsorbent and made of the traditional pulp and binder fiber can experience xe2x80x9cwet collapsexe2x80x9d. This occurs as a result of saturation of the pulp and the subsequent inability to regenerate void space as fluid is added to the structure. The binder fibers, generally synthetic polymer fibers that are naturally hydrophobic, contribute to this problem since they interfere with the wicking performance of the structure due to their poor wettability. In addition, the constraints induced by the bonding of the binder fibers restrains expansion of the absorbent structure, further reducing void volume and decreasing the ultimate capacity of the material. If the structure were able to wick fluid away from the area of incipient wet collapse more efficiently, the phenomenon might be avoided completely.
A material which treads the fine line between wet collapse and gel blocking would be very desirable. Such a material would avoid the undesirable features of uncontrolled superabsorbent expansion while efficiently absorbing fluids. It would also avoid wet collapse by maintaining a sufficient pore structure, allowing liquid to continue moving through it. Such a material would exhibit high levels of multi-functional absorbent performance.
In response to the discussed difficulties and problems encountered in the prior art, a new structural composite comprising integrated layers for use in personal care products has been developed. In this material, at least one layer having a mixture of pulp, superabsorbent in an amount between 1 and 30 weight percent and binder in an amount between 1 and 6 weight percent, is adjacent a layer having a very high superabsorbent concentration. There may be alternating layers of similar composition. The overall amount of binder within the structure is at most 4 weight percent and the overall amount of superabsorbent within the structure is between 35 and 80 weight percent. The structure is then compacted to a density of between about 0.1 to 0.3 g/cc. These layered structures have better intake properties than traditionally made competitive materials. These structures surprisingly also have better distribution properties than competitive materials, presumably due to the avoidance of gel blocking, capillary disruption and wet collapse.
Another way of describing this material is as having from two to nine alternating A and B layers where the A layers are a mixture of pulp, binder in an amount between 1 and 6 weight percent and superabsorbent in an amount between 1 and 30 weight percent, and the B layers haver a superabsorbent concentration of at least 80 weight percent. The overall material also has binder in an amount of at most 4 weight percent and superabsorbent in an amount between 35 and 80 weight percent, is compacted to a density of between about 0.1 to 0.3 g/cc and has a basis weight between 80 and 1200 gsm.
The amount of superabsorbent in the A layer is more particularly between 5 and 28 weight percent and still more particularly between 15 and 25 weight percent.
The layered material may have an even number of layers or an odd number of layers. If the layered material has an odd number of layers the outermost layers may be A or B layers. More particular embodiments of the layered material may have 5 layers and a basis weight between 200 and 667 gsm and 7 layers and a basis weight between 280 and 934 gsm.
These materials are suitable for use in personal care products like diapers, training pants, incontinence products, bandages, and sanitary napkins.